Upright type bushing current transformer

ABSTRACT

A bushing current transformer is provided and includes an auxiliary current transformer mounted on the top of a bushing. The primary and secondary coils of the auxiliary current transformer are connected parallel to each other and in series to an electrical power line having a high voltage and carrying a high current therethrough. A conductive lead is connected to the secondary coil of the auxiliary current transformer and is conducted to the bottom of the bushing to thereby form a primary coil of a main current transformer which is positioned on the bottom of the bushing and then conducted upwards again through the bushing. With such an arrangement the size of the line conductor being introduced into the bottom of the bushing can be made smaller, since the current transformation ratio between the primary and secondary coils of the auxiliary current transformer can be adjusted. Also, the current transformer can be standardized and thereby adapted for mass production due to the ability to fix the secondary current of the auxiliary current transformer at a constant amplitude.

United States Patent [151 3,668,513 Tsubouchi et a1. June 6, 1972 54]UPRIGHT TYPE BUSI-HNG CURRENT FOREIGN PATENTS OR APPLICATIONSTRANSFORMER Inventors: Denji Tsubouchi; Susumu Ito, both of Yokohama;Eisuke Toyota, Hiratsuka;

Kenji Wada, Yamato, all of Japan Assignee: Co.,

Tokyo Shibaura Electric Kawasaki-shi, Japan Filed: Mar. 19, 1971 Appl.No.: 126,121

Ltd.,

Foreign Application Priority Data Mar. 31, 1970 Japan ..45/26883References Cited UNITED STATES PATENTS AttorneyOblon, Fisher & Spivak[57] ABSTRACT A bushing current transformer is provided and includes anauxiliary current transfonner mounted on the top of a bushing. Theprimary andsecondary coils of the auxiliary current transformer areconnected parallel to each other and in series to an electrical powerline having a high voltage and carrying a high current therethrough. Aconductive lead is connected to the secondary coil of the auxiliarycurrent transformer and is conducted to the bottom of the bushing tothereby form a primary coil of a main current transformer which ispositioned on the bottom of the bushing and then conducted upwards againthrough the bushing. With such an arrangement the size of the lineconductor being introduced into the bottom of the bushing can be madesmaller, since the current transformation ratio between the primary andsecondary current transformer can be adjusted. Also, the currenttransformer can be standardized and thereby adapted for mass productiondue to the ability to fix the secondary current of the auxiliary currenttransformer at a constant amplitude.

6 Claims, 5 Drawing Figures coils of the auxiliary PAIENTEDJuu 6|9723,668,513

SHEET 2 OF 2 1 UPRIGIIT'I'YIII BUSHING CURRENT TRANSFORMER BACKGROUND OFTHE INVENTION 1. Field Of The Invention The present invention generallyrelates to an upright type bushing current transformer, and moreparticularly to a bushing current transformer which is adapted for massproduction.

2. Description Of The Prior Art In the past, upright type bushingcurrent transformers,

.which were employed in AC. electrical power circuits for measuring thecurrent amplitude of the circuit, have generally bottom portion of aninsulating tube or bushing and a conductor to be connected in series toa line conductor was conductedfrom the top of the bushing into thebottom portion thereof to form a primary coil of the transformerassembly and then conducted upwards again through the bushing. Thebushing used in the upright type bushing current transformer for highvoltage use was located relatively high in order to resist against thehigh line voltage present. As a consequence thereof, the aforesaidconductor being directed into the bushing had to be of a relatively longlength. Moreover, when the bushing type current transformer was used formeasuring large currents, the conductor was required to have a largecross-section in order to enable a large current to pass therethrough.Thus, the prior art type bushing current transformer was usually quiteexpensive. 7

In order to eliminate some of the aforesaid drawbacks, a prior artupright type bushing current transformer was developed which included atransformer assembly mounted on the insulating tube or bushing. In'thistype of assembly, a conductor was connected in series to a lineconductor and then merely extended through a window of aniro n core ofthe transformer assembly mounted on the top of the bushing. As such, thelength of the conductor was reduced to a much shorter length. However,again while somewhat satisfactory, because the transformer assembly hada large weight, it was found that with the bushing current transformermounted on top of the transformer assembly, the same was top heavy andtherefore undesirable from an earthquake-proof point of view.

' SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to provide a new and improved unique bushing type currenttransfonner wherein the main current transformer thereof may be readilyemployed without changes being made thereto with electrical lines havingdifferent current ratings.

Another object of the present invention is to provide a new and improvedunique upright type bushing current trans former wherein the same may bereadily standardized and thereby reduce the manufacturing cost thereof.

Still another object of this invention is to provide a new and improvedunique upright type bushing current transformer for measuring a linecurrent having a large amplitude and wherein a conductive lead having arelatively small cross-section is directed into the bushing thereof toform a primary coil of a main current transformer located at a bottomportion of the bushing.

Yet one other object of the present invention is to provide a new andimproved unique upright type bushing current transformer which isrelatively immune to damage from earthquakes.

Briefly, in accordance with this invention, these and other objects are,in one aspect, attained by the provision of an auxiliary currenttransformer mounted on the top of an insulating tube or bushing. Theprimary and secondary coils of the auxiliary current transformer haveconductors which extend through a window of an iron core. The primaryand secondary coils are wound in opposite directions with respect tocurrent flow therethrough and are further connected in parallel to eachother. The parallelly connected primary and secondary coils of theauxiliary current transformer are then connected housing provided and isthen conducted upwards through the bushing.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be morefully understood from the following description when taken in connectionwith reference to the accompanying drawings, wherein:

FIG. 1 is a front sectional view, partly broken away, of a preferredembodiment of an upright type bushing transformer according to thepresent invention;

FIG. 2 is an equivalent circuit diagram of the bushing currenttransformer of FIG. 1;

FIG. 3 is an equivalent circuit diagram of the bushing currenttransformer of another and alternative embodiment of the presentinvention; I

FIG. 4 is a circuit diagram of the bushing current transformer of stillanother and alternative embodiment of the present invention; and,

FIG. 5 is a circuit diagram of one other alternative embodiment of thebushing current transformer of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to thedrawings, wherein like reference numerals designate identical orcorresponding parts throughout the several views, and more particularlyto FIG. 1 thereof,wherein an upright type bushing current transformer isgenerally shown with a reference numeral 10, and the same includes abottom casing 11, a main current transformer 12 mounted therein, anupright insulating tube or'bushing 13 mounted on the casing 1 1, anauxiliary current transformer 14 removably mounted on the top of theupright bushing I3, and a housing 15 which sealingly encloses theauxiliary current transformer 14 therein.

The auxiliary current transformer 14 includes a conventionally woundiron core 16 having a window 17 through which a primary coil 18 extends.The opposite ends of the primary coil 18 extend through a pair ofinsulators l9 and 20 mounted on the side walls of the housing 15, andhave a pair of terminals 21 and 22 which are connected to the ends ofelectrical power lines (not shown). The auxiliary current transformer 14also has a secondary coil 23 which is wound around the iron core 16 andthe same has a pair of end terminals that are respectively connected tothe opposite end portions of the primary coil 18. through leadconductors 24 and 25 provided along the outside area of the window 17.Thus, it should be apparent that the primary and secondary coils l8 and23 have been connected in parallel with each other.

Now let us assume, for example, that an electrical current flow ispresent during a half cycle of A. C. and flows from terminal 21 toterminal 22. It can be understood from FIG. 1 with respect to thedirection of current flow, that the primary coil 18 extends through thewindow 17 of the core 16 from the left side to the right side, while thesecondary coil 23 extends through the window 17 from the right side tothe left side. Thus, it should be understood that the primary andsecondary coils 18 and 23 are wound around the core 16 in oppositedirections to each other, and are connected in parallel. Also, it shouldbe understood that the line currents flowing through the primary coil 18and the leads 24 and 25 will be in the same 'and respective primaryand'secondary coils 32 and 33 which are wound thereon. The iron core 31is supported on the base of the casing 11 by an insulating support 35.The conductive lead 28 is directed downward through the bushing 13 andthen wound around the core 31 through a window 34 provided in the coreto thereby form the primary coil 32. The end of the primary coil 32 isthen returned upward by the conductive lead 25 which also extendsthrough the bushing 13.

The main current transformer assembly 12, which includes the core 31,the primary and secondary coils 32 and 33 and the pairof lead.conductors 28 and 25, may be molded in a resinous insulation 36.

It should be understood that a conventional condenser cone 40 isprovided around the high tension lead conductors 25 and 28, as well asthe main transformer assembly 12, to thereby restrain the potentialgradient.

While not shown, it should be apparent that a suitable insulating andcooling fluid, such, for example, as mineral oil and gaseous sulphurhexafluoride (SF,,) is filled within the casing II and the bushing 13.

The output from the secondary coil 33 of the main current transformer 12is provided at a pair of terminals 37 and 38 which are mounted onthe'side of the casing 11, and the same may be employed to energize anysuitable device such, for example, as meters, protecting relays and thelike.

The equivalent circuit diagram of the upright bushing currenttransformer 10 of FIG. 1 is shown in FIG. 2.

From FIG. 2, it is clearly seen that the primary and secondary'coils 18and 23 of the auxiliary current transformer 14 are connected in parallelwith each other and in series with an electrical power line (not shown)through the terminals 21 and 22. I

' Assuming now that the number of turns of the primary coil 18 of theauxiliary current transformer 10 is one turn, the number of turns of thesecondary coil 23 is nine turns, and the amplitude of the rated currentis 4,000 amperes, then a reduced current of 400 amperes willbe-applied-through the secondary coil 23 and the remaining 3,600 ampereswill be applied through the primary coil 18. Accordingly, the reducedcurrent of 400 amperes will be applied through the primary coil 32 ofthe main current transformer 12 along the lead conductors 28 and 25. Inthis case, a rated current, such as amperes, may be provided at theterminals 37 and 38 of the secondary coil 33 of the main currenttransformer 12.

When, for example, the rated line current has an amplitude of 2,000amperes, the intermediate tap 26 may be employed instead of the tap 27in order to change the number of turns of the secondary coil 23 of theauxiliary current transformer 14 from the aforesaid value of nine turnsto four turns. Thus, with such a change, it will be apparent that thecurrent amplitude of the secondary coil 23 will have the same amplitude,namely, 400 amperes, but that the current amplitude of the primary coil18 will have an amplitude of 1,600 amperes.

It will thus be apparent that according to the present invention a maincurrent transformer 12 having the same rating may be readily employedwith electrical power lines having-different current ratings.

It can be further seen that according to the present invention anauxiliary current transformer 14 can be easily altered to another ratingwithout requiring any changes to the main current transformer assembly12. Accordingly, a main current transformer assembly 12 having a givencurrent rating, size and construction can be readily employed for usewith power lines havingdifferent current ratings.

In accordance with the above, main current transformer assemblies, suchas the transformer assembly 12, can be readily standardized with theattendant advantages of reduction in manufacturing cost of the uprighttype current transformers, since the same can be adapted for massproduction.

Moreover, it can be seen that since the main current transformer 12 ofthe present invention is located at the bottom portion of the bushing 13that the center of gravity of the upright type current transformerassembly 10 will be at a low position and thereby enable an effectiveresistance against earthquakes and the like.

It will be further apparent that in accordance with the presentinvention, since a reduced current can be supplied to the primary coil32 of the main current transformer 12 through the lead conductors 25 and28 that the sectional areas of the lead conductors 25 and 28, as well asthat of the primary coil 32, can be effectively reduced and thereby savethe quantity of copper or aluminum required for the same.

Referring now to FIG. 3, an alternative embodiment of the presentinvention is shown with the auxiliary current transformer 14 having apair of secondary coils 230 and 330 each of which have the same numberof turns. Thus, it is possible to employ the auxiliary transfonner 14 intwo different ways by selecting either a series connection or a parallelconnection of the pair of coils 230 and 330.

Referring now to FIG. 4, a further alternative embodiment of the presentinventionis shown with an additional auxiliary current transformerhaving a primary coil and a secondary coil 430, similar to that-of FIG.1, being connected in series with the secondary coil 23 of the auxiliarycurrent transformer 14. Thus, the circuit of FIG. 4 may by employed foreither providing a more reduced current at the lead conductors 25 and26, or for enabling measurement of a line current having an extremelyhigh amplitude.

. Referring now to FIG. 5, one other alternative embodiment of thepresent invention is shown with an impedance element 39 being connectedacross the secondary coil 23 of the auxiliary current transformer 14 forenabling a fine adjustment of the current flowing therethrough to bemade. The impedance element 39 may be either of the variable or fixedtype, and may be connected across the primary coil 18 of the auxiliarycurrent transformer 14.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto beunderstood that within the scope of the appended claims theinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. An upright type bushing current transformer comprising:

a casing;

a main current transformer mounted in said casing and having an ironcore with a primary and a secondary coil wound thereon:

an upright bushing mounted on said casing;

an auxiliary current transformer mounted on the top of said bushing andhaving an iron core with a primary and a secondary coil wound thereon,the windings being in opposite directions and said primary and secondarycoils of said auxiliary current transformer being connected in parallelwith each other and being connected in series to an electrical powerline; and,

a conductive lead connected to said primary of said main transformer andsaid secondary of said auxiliary transformer and extending through saidbushing for enabling energization of the primary coil of said maincurrent transformer in accordance with the current of the secondary coilof said auxiliary current transformer. v

2. An upright type bushing current transformer according to claim 1,wherein said auxiliary current transformer is removably mounted on claim1, wherein the topofsaid ushing said secondary coil of the auxiliarycurrent transformer inp bushing cunenf "ansformer ifccol'dmg to cludes asecond auxiliary current transformer connected claim 1, wherein saidsecondary coil of the auxiliary current i Series there;

transformer includes at least one intermediate tap for enabling 5different current transformations to be realized.

4. An upright type bushing current transformer according to at least oneof Said primary and Secondary cons of Said claim 1, wherein saidsecondary coil of the auxiliary current transformer innary currenttansformer Includes an Impedance element eludes at least two coilelements which may be connected l0 :snnected therzlcross enabling a fineadjustment of either in series or in parallel. e current can ormanon tooccur 5. An upright type bushing current transformer according to 6. Anupright type bushing current transformer according to claim 1, wherein

1. An upright type bushing current transformer comprising: a casing; amain current transformer mounted in said casing and having an iron corewith a primary and a secondary coil wound thereon: an upright bushingmounted on said casing; an auxiliary current transformer mounted on thetop of said bushing and having an iron core with a primary and asecondary coil wound thereon, the windings being in opposite directionsand said primary and secondary coils of said auxiliary currenttransformer being connected in parallel with each other and beingconnected in series to an electrical power line; and, a conductive leadconnected to said primary of said main transformer and said secondary ofsaid auxiliary transformer and extending through said bushing forenabling energization of the primary coil of said main currenttransformer in accordance with the current of the secondary coil of saidauxiliary current transformer.
 2. An upright type bushing currenttransformer according to claim 1, wherein said auxiliary currenttransformer is removably mounted on the top of said bushing.
 3. Anupright type bushing current transformer according to claim 1, whereinsaid secondary coil of the auxiliary current transformer includes atleast one intermediate tap for enabling different currenttransformations to be realized.
 4. An upright type bushing currenttransformer according to claim 1, wherein said secondary coil of theauxiliary current transformer includes at least two coil elements whichmay be connected either in series or in parallel.
 5. An upright typebushing current transformer according to claim 1, wherein said secondarycoil of the auxiliary current transformer includes a second auxiliarycurrent transformer connected in series thereto.
 6. An upright typebushing current transformer according to claim 1, wherein at least oneof said primary and secondary coils of said auxiliary currenttransformer includes an impedance element connected thereacross forenabling a fine adjustment of the current transformation to occur.